Sep 25, 2012 Here is a project I have had on the back burner for a while. Skip navigation Sign in. Wico EK Magneto Repair magnet charger 16of - Duration: 12:24. Shopdogsam 17,689 views. Oct 28, 2010 - The ability of magnetorheological(MR) fluids to resist compression in the direction of. Small energy and wide working temperature range make MR fluids. The magnetizer that fixed the lower plate is connected to the force.
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Design of Tunnel Magnetoresistive-Based Circular MFL Sensor Array for the Detection of Flaws in Steel Wire Rope
College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing, China
Received 27 January 2016; Revised 24 July 2016; Accepted 15 August 2016
![Magneto Magneto](/uploads/1/2/5/6/125690611/231482309.png)
Academic Editor: Eugenio Martinelli
Copyright © 2016 Liu Xiucheng et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Tunnel magnetoresistive (TMR) devices have superior performances in weak magnetic field detection. In this study, TMR devices were first employed to form a circular magnetic flux leakage (MFL) sensor for slight wire rope flaw detection. Two versions of this tailor-made circular TMR-based sensor array were presented for the inspection of wire ropes with the diameters of 14 mm and 40 mm, respectively. Helmholtz-like coils or a ferrite magnet-based magnetizer was selected to provide the proper magnetic field, in order to meet the technical requirements of the TMR devices. The coefficient of variance in the flaw detection performance of the sensor array elements was experimentally estimated at 4.05%. Both versions of the MFL sensor array were able to detect multiple single-broken wire flaws in the wire ropes. The accurate axial and circumferential positions of these broken wire flaws were estimated from the MFL scanning image results. In addition, the proposed TMR-based sensor array was applied to detect the MFL signal induced by slight surface wear defects. A mutual correlation analysis method was used to distinguish the signals caused by the lift-off fluctuation from the MFL scanning image results. The MFL sensor arrays presented in this study provide inspiration for the designing of tailor-made TMR-based circular sensor arrays for cylindrical ferromagnetic structural inspections.
1. Introduction
In recent years, magnetoresistive (MR) devices have been integrated into minimalistic sensors for nondestructive testing applications [1, 2]. Compared to inductive coils, the MR-based sensors can operate in ultralow frequency ranges with impressive signal to noise ratios (SNR). With its high spatial resolution and high sensitivity to weak magnetic fields, the MR-based scanning eddy currents or magnetic flux leakage (MFL) sensors can successfully detect the surface or subsurface cracks in conductive or ferromagnetic materials [3, 4]. As the newest member of the MR family, the tunnel magnetoresistive (TMR) device has been reported to demonstrate superior performance compared to the anisotropic magnetoresistive (AMR) and giant magnetoresistive (GMR) devices [5]. As per the latest publications, TMR-based scanning eddy current systems have the ability to detect surface notches with dimensions as low as a 400 μm length, 30 μm width, and 30 μm depth in titanium alloy samples [6]. The strength of the magnetic field induced by the eddy current generally is located in the limited linear operation range of the TMR. However, in regard to the magnetic flux leakage (MFL) detection in ferromagnetic materials, the magnetizer needs to be carefully deployed in order to avoid saturation of the TMR in the applied magnetic or flux fields which were induced by the defects. Excitation coils with lower DC currents or surrounding magnetic shield structures are commonly employed to create the proper magnetic environment for TMR devices [7, 8].
In our previous research, a single TMR-based MFL detection system was developed for the detection of flaws in hoist wire ropes [9]. The MFL signal induced by a single broken wire (0.5 mm in diameter) in a 14 mm wire rope could be clearly recognized from the oscillation signal which was generated by the twisted rope’s surface. In addition, the minimal angular detection range for a single TMR element was estimated, and it was determined that it was insufficient to cover the outside surface of the entire wire rope. Therefore, a circular sensor array needed to be developed for the practical inspection of steel wire ropes.
In this study, TMR devices were used to form circular sensor arrays for detecting the MFL signals induced by defects in steel wire ropes with a diameter of 14 mm and 40 mm, respectively. An electromagnetic magnetizer and a permanent magnetic circuit were deployed for the two sensor arrays. Finally, multiple single-broken wire flaws and wear defect detection, as well as their visualization, were successfully accomplished using the proposed TMR-based sensor array.
2. TMR-Based Sensor Array for the MFL Method
2.1. Design of the Circular MFL Sensor Array
Magnetic dipole and finite element methods are commonly used to analyze the induced magnetic flux leakage field (FLL) distribution at a defect in a structure [10]. In this study, the single-broken wire and axial wear defects in wire ropes were the focus. According to the published results on this topic, the components of FLL at both the axial and radial directions of a wire rope are usually studied for defect extent characterizations [11]. Figure 1 shows both the axial and radial component of the FLL induced by local flaws (such as broken wires and pitting defects), along with the loss of metallic area defects (such as wear and corrosion).